In typical computed tomography systems, X-rays, generated by an X-ray source, are collimated to form a fan beam that is transmitted through an imaged object to an X-ray detector array orientated within the imaging plane. The detector array is comprised of detector elements which each measure the intensity of transmitted radiation along a ray projected from the X-ray source to that particular detector element. The X-ray source and detector array are typically rotated on a gantry within the imaging plane, around the imaged object, so that the fan beam intercepts the imaged object at different angles. At each angle, a projection is acquired comprised of the intensity signals from each of detector elements. The gantry is then rotated to a new angle and the process is repeated to collect a number of projections at different angles to form a tomographic projection set. In alternate tomography systems, the detector array remains fixed and comprises a 360 degree ring of detectors and the source is moved arcwise around the imaged object through 180 degrees plus the fan beam angle or more of arc. In such systems, only the X-ray source is rotated to acquire the tomographic projection set.
The time and expense of a tomographic study increases with the number of slices required. The time required to collect the data for a series of slices depends in part on aspects such as a) the time required to accelerate the gantry to scanning speed, b) the time required to obtain a complete tomographic projection set, c) the time required to decelerate the gantry and d) the time required to reposition the object in the z-axis for the next slice. Reducing the time required to obtain a full slice series may be accomplished by reducing the time required to complete any of these four steps. Additionally, movement of the object under inspection as well as the motion of the X-ray source and/or detector array, using the gantry, results in creation of unacceptably high levels of artefact in reconstructed images.
Accordingly, there is need in the prior art to reduce the overall time of conducting a tomographic inspection. There is also need to improve the overall imaging quality of tomographic inspection by addressing causes leading to image artefacts—particularly those induced by physical motion of the source-detector assembly.